Ethernet switches ease shift to multi-port GPON line cards

Calabasas, Calif.With input from customer Broadlight Corp. and the technology prowess to pull it off, Fulcrum Microsystems developed the first Ethernet switches that are targeted at multi-port optical line termination (OLT) cards for Gigabit Passive Optical Network (GPON) equipment.

The FM2103 and FM2104 switches join Fulcrum's FocalPoint family of devices, all of which are based on a shared memory architecture. The FM2103 is configured for four-port OLT cards with four 2.5-Gbit Ethernet ports for access connections and two 10-Gbit Ethernet XAUI ports for backbone links. The FM2104 is for eight-port OLT boards and features eight 2.5-Gbit Ethernet ports with two 10-Gbit Ethernet XAUI ports.

The FM2103 and FM2104 switches are designed to make it easier for equipment manufacturers to migrate from single to multi-port interfaces in OLT cards.

Both devices feature flexible header processing for Ethernet-to-GPON networking, allowing the FM2103 and FM2104 to parse the GPON-specific packet header.

While the shared memory architecture concept is not new, the way that Fulcrum implemented the switch element data path is proprietary.

"The whole design flow is a proprietary process and it does use that event-driven logic, which provides a very fast data path and it also has the unusual principle of operation in that does not dissipate energy unless data is flowing through it," said Bud Noren, senior product manager. "Unlike other circuit elements where a clock will constantly be sent to it and will burn data even when there's no data going through it. That's where we get that lower power."

The FM2103 and FM2104 have a typical power dissipation of less than 10-watts and 9-watts, respectively. When they are functioning at the 10-Gbit mode, they dissipate approximately 1-watt per port. The power dissipation is determined by the amount and type of data flowing through it:it could be lower or higher.

The FM2103 and FM2104 can achieve equivalent clock speeds of more than 700-MHz with Taiwan Semiconductor Manufacturing Corp.'s 1.3-micron process. "Others will have a challenge achieving one-third of that speed with that process," Noren said.

The BroadLight deal
Fulcrum and BroadLight, Mountain View, Calif., are working together to develop an integrated GPON product consisting of FocalPoint devices and BroadLight OLT controllers. For more on BroadLight's products, click here: www.broadlight.com

"They recognized that there are some features in our switch that work quite well with their optical line termination controller chip," Noren said.

Indeed, the most notable Layer-2 function of the FM2103 and FM2104 is proprietary header support. GPON uses a header called GPON encapsulation method (GEM) in which all traffic is mapped across the network using a variant of SONET/SDH generic framing procedure. It can natively transport voice video and data without an ATM or IP encapsulation layer. That's why GPON can offer downstream bandwidth utilization rates as high as 2.5-Gbits/s.

"GEM is a header format that is peculiar to passive optical networks. And when that header enter BroadLight's OLT controller chip, they change it in a way and make a proprietary header of their own type out of it," Noren explained. "Even though our switch chip is a standard Ethernet switch, it has the ability to examine other types of headers."

As a result, it can actually skip to certain areas within a packet, look at the different packet header and react on it.

Another key Layer-2 function pertinent to working with BroadLight's OLT controller includes spanning tree, a method in which a Layer 2 switch can act on Layer 3 information to make more intelligent forwarding conditions, as well as relieve congestion.

The FM2103 and FM2104 are packaged in a 897-ball BGA and sampling now. Production volumes will be available based on market demand. In volume quantities, the FM2103 and FM2104 cost less than $150 and $175, respectively.